Micelle formation in aqueous n-alkanoate solutions: A fourier transform infrared study

Abstract

The concentration dependencies of the infrared spectra of deuterium oxide solutions of sodium propionate, n-butyrate, n-pentanoate, n-hexanoate, n-heptanoate, n-octanoate, nnonanoate, and n-decanoate have been determined in concentration ranges encompassing the critical micelle concentrations. Progressively decreasing premicellar aggregation with increasing acyl chain length is demonstrated, with there being no evidence for premicellar aggregation in the sodium octanoate, nonanoate, and decanoate solutions. The frequencies and widths of the C-H stretching bands indicate that the acyl chains are conformationally disordered in the micellar phase, to a degree similar to that in liquid alkanes. They also indicate that, in the micellar phase, there is little or no hydrocarbon chain-water contact.